1. Field of the Invention
This invention relates to pneumatic belted tires for motorcycles. More particularly it relates to an improvement of a belt structure in this type of tire which ensures tire performance inherent to the motorcycle and particularly realizes the effective enhancement of straight running performance without deterioration of cornering performances.
2. Related Art Statement
The development of pneumatic belted tires for motorcycles has been actually backward as compared with pneumatic belted tires for four-wheeled vehicles. This is because of the cornering properties inherent to the motorcycle or peculiar behaviors under a unique driving operation capable of effecting the turning by a camber angle, which is different from the case of ordinary passenger cars.
For this reason, when a predetermined camber angle is given to a tire for motorcycle having the same belt structure as the tire for passenger car, not only is the smooth tread gripping never obtained due to the rigidity of the central portion of the belt and the discontinuity of rigidity near the belt end, but also the feeling of weak stiffness appears during the cornering, which cause troubles in the steering response and stability.
As a countermeasure against the above problems, there has been proposed a belt composed of a belt layer containing cords arranged substantially in parallel to the mid-circumference of the tire (hereinafter referred to as a circumferential cord) in Japanese Utility Model laid open No. 58-160,805.
Such a belt structure certainly enables the smooth cornering and is advantageous in the steering response and the stability. However, since the belt layer is formed by helically winding a single circumferential cord from one widthwise end of a tire tread to the other end thereof, the circumferential cord is regularly inclined at an extremely small angle (.theta.) with respect to the mid-circumference of the tire, which brings about the occurrence of plysteer in the straight running together with a relatively thin tread rubber peculiar to the tire of this type and tends to obstruct straight running performance.
Further, a step of helically winding the single cord over a region extending from one widthwise end of the tread to the other end thereof is complicated, which is unfavorable from a viewpoint of the productivity.